A torque converter is a hydrodynamic unit that transfers torque between an engine and an automatic transmission. The torque converter generally includes a torque converter pump (driving member), a turbine (a driven member), and a stator that are disposed in a housing full of hydraulic fluid. The torque converter pump is generally disposed at a rear portion of the housing (away from the engine), and it turns with a crankshaft of an engine. The turbine is generally disposed at a front portion of the housing (near the engine), and is connected to a transmission input shaft. The turbine is free to rotate independently from the torque converter pump.
The hydraulic fluid flows from the torque converter pump toward the turbine in a radial outer portion of the torque converter. The hydraulic fluid then flows from the turbine back toward the torque converter pump by way of the stator in a radial inner portion of the torque converter. At low torque converter speed ratios, redirection of the hydraulic fluid by the stator causes torque multiplication thereby improving vehicle performance. However, at higher torque converter speed ratios, the transfer of torque through the torque converter becomes inefficient and impairs fuel economy.
In order to optimize vehicle efficiency, the torque converter may be “locked” after a predefined torque converter speed ratio is reached such that the torque converter pump and turbine are mechanically coupled and rotate together. A “lock-up” clutch is therefore commonly provided to lock the torque converter and thereby optimize efficiency. The lock-up clutch may be an electronically controlled converter clutch (hereinafter ECCC) configured to lock-up completely or to selectively slip in a controllable manner. Therefore, the ECCC can absorb a portion of an engine torque spike by controlled slipping to provide smoother vehicle operation. In other words, the ECCC may be programmed to slip by an amount necessary to prevent the engine torque spike from being transferred to the transmission.